生成24位字符串ID__IdGenerator.java

import java.net.NetworkInterface;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.Enumeration;

/**
* 生成24位字符串ID
*
*/
public class IdGenerator implements Comparable<IdGenerator> {

/**
* 调用该方法获取24位字符串ID
* @return
*/
public static String get() {
return new IdGenerator().toString();
}

public IdGenerator() {
_time = _gentime;
_machine = _genmachine;
synchronized (_incLock) {
_inc = _nextInc++;
}
_new = true;
}

public int hashCode() {
return _inc;
}

public String toStringMongod() {
byte b[] = toByteArray();

StringBuilder buf = new StringBuilder(24);

for (int i = 0; i < b.length; i++) {
int x = b[i] & 0xFF;
String s = Integer.toHexString(x);
if (s.length() == 1)
buf.append("0");
buf.append(s);
}

return buf.toString();
}

public byte[] toByteArray() {
byte b[] = new byte[12];
ByteBuffer bb = ByteBuffer.wrap(b);
bb.putInt(_inc);
bb.putInt(_machine);
bb.putInt(_time);
reverse(b);
return b;
}

static void reverse(byte[] b) {
for (int i = 0; i < b.length / 2; i++) {
byte t = b[i];
b[i] = b[b.length - (i + 1)];
b[b.length - (i + 1)] = t;
}
}

static String _pos(String s, int p) {
return s.substring(p * 2, (p * 2) + 2);
}

public String toString() {
return toStringMongod();
}

public int compareTo(IdGenerator id) {
if (id == null)
return -1;

long xx = id.getTime() - getTime();
if (xx > 0)
return -1;
else if (xx < 0)
return 1;

int x = id._machine - _machine;
if (x != 0)
return -x;

x = id._inc - _inc;
if (x != 0)
return -x;

return 0;
}

public int getMachine() {
return _machine;
}

public long getTime() {
long z = _flip(_time);
return z * 1000;
}

public int getInc() {
return _inc;
}

final int _time;
final int _machine;
final int _inc;

boolean _new;

static int _flip(int x) {
byte b[] = new byte[4];
ByteBuffer bb = ByteBuffer.wrap(b);
bb.order(ByteOrder.LITTLE_ENDIAN);
bb.putInt(x);
bb.flip();
bb.order(ByteOrder.BIG_ENDIAN);
return bb.getInt();
}

private static int _nextInc = (new java.util.Random()).nextInt();
private static final String _incLock = new String("IdGenerator._incLock");

private static int _gentime = _flip((int) (System.currentTimeMillis() / 1000));

static final Thread _timeFixer;
private static final int _genmachine;
static {
try {
final int machinePiece;
{
StringBuilder sb = new StringBuilder();
Enumeration<NetworkInterface> e = NetworkInterface.getNetworkInterfaces();
while (e.hasMoreElements()) {
NetworkInterface ni = e.nextElement();
sb.append(ni.toString());
}
machinePiece = sb.toString().hashCode() << 16;
}

final int processPiece = java.lang.management.ManagementFactory.getRuntimeMXBean().getName().hashCode() & 0xFFFF;
_genmachine = machinePiece | processPiece;
} catch (java.io.IOException ioe) {
throw new RuntimeException(ioe);
}

_timeFixer = new Thread("IdGenerator-TimeFixer") {
public void run() {
while (true) {
try {
Thread.sleep(499);
} catch (InterruptedException e) {
}
_gentime = _flip((int) (System.currentTimeMillis() / 1000));
}
}
};
_timeFixer.setDaemon(true);
_timeFixer.start();
}

}